Hydraulic drilling jar

ABSTRACT

A jar especially designed to withstand the high torques and abuse produced by deflections of the well bore from vertical encountered in deep well drilling. Both spline and hammer-anvil faces are below and outside of the zone occupied by the jar dashpot system, whereby torque and jar impact strains are not transmitted through the outer mandrel portion housing said system. Torque and jar impact strains are transmitted throughout the tool through a beefed up internal mandrel integral from end to end. Furthermore, said strains are transmitted through only a single threaded joint connecting the lower end of the outer mandrel to the bottom sub of the tool. In addition, the jar is stabilized at four axially spaced points therein by arrangements causing the inner mandrel to smoothly journal in the outer mandrel thus uniting their strength at these points.

United States Patent Downen Apr. 15, 1975 HYDRAULIC DRILLING JAR [76] Inventor: Jim L. Downen, 2931 Pierce Rd., [57] ABSTRACT Bakersfield, Calif. 93308 A ar especlally deslgned to withstand the high torques Filed: June 1974 and abuse produced by deflections of the well bore [21] APPL NO; 481,552 from vertical encountered in deep well drilling. Both spline and hammer-anvil faces are below and outside of the zone occupied by the jar dashpot system, US. Cl. whereby torque and jar impact trains are not trans- [5 d through the outer mandrel portion housing aid Fleld f sealCh ystem Torque and jar impact strains are transmitted throughout the tool through a beefed up internal man- References Clted drel integral from end to end. Furthermore, said UNITED STATES PATENTS strains are transmitted through only a single threaded 2,645,459 7/1953 Sutliff 175 297 joint Connecting the lower end of the Outer mandrel to 3,083,533 /1963 Sutliff 175 297 th b tt m su of the tool. 3,221,826 12/1965 Webbw "5/297 In addition, the jar is stabilized at four axially spaced 3388755 6/1968 75/297 points therein by arrangements causing the inner 3,539,025 11/1970 Sutllff 175/297 mandrel to smoothly ournal 1n the outer mandrel thus 3,566,981 3/1971 Love 175/297 3 570 612 3/1971 Slator 175/297 mung Strength at Points- Primary Examiner-James A. Leppink 8 Clalms 16 Drawmg Figures 7 1 1' 966 1 afi/ -a fao g 1 l a fil 28- m a J ll1 v 29 PATENTEDAPR 1 51975 4 SHEET 3 p55 5 A L 70 r 774 HYDRAULIC DRILLING JAR SUMMARY OF THE INVENTION It is a general object of the invention to provide a hydraulic jar which will excell in ruggedness jars previously available for and employed in deep well drilling.

Another object is to increase the capacity of the jar to endure jar impact and torque strains by channelling these strains preponderantly through the inner mandrel and then uniformly beefing up the inner mandrel and building this and the upper jar sub in one integral piece.

A further object is to reinforce the inner mandrel against bending strains due to direction changes in the well bore, by snuggly journalling the inner mandrel in the outer mandrel at frequent axially spaced points in the jar.

Still another object of the invention is to provide such a jar having a novel, long wearing, dashpot valve sleeve including tandem sections, one of which tightly fits the outer mandrel wall and the other of which sloppily fits a cylindrical surface provided on the inner mandrel to provide an escape orifice for the dashpot liquid.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical sectional view partly broken away of a preferred embodiment of the invention with the parts thereof fully extended as at the moment of strik ing a jarring blow.

FIGS. 2 to 5 inclusive are half vertical sectional views of consecutive portions of FIG. 1 taken on line 25/- 25.

FIGS. 6 to 9 inclusive are views similar respectively to FIGS. 2-5 with the parts of the invention fully retracted as when drilling with the drill resting on the bottom of the hole.

FIG. 10 is a cross sectional view taken on the line 10-10 of FIG. 2.

FIG. 11 is a cross sectional view taken on the line 11-11 of FIG. 3.

FIG. 12 is a cross sectional view taken on the line l212 of FIG. 3.

FIG. 13 is a cross sectional view taken on the line 13-13 of FIG. 4.

FIG. 14 is a cross sectional view taken on the line 14l4 of FIG. 5.

FIG. 15 is a double enlarged sectional view of encircled portion in FIG. 3.

FIG. 16 is a cross sectional view taken on the line l616 of FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring specifically to the drawings and particularly to FIGS. 1-5 inclusive, the invention is shown therein as embodied in a hydraulic jar 20 which is particularly useful in the drilling of deep oil wells. The jar 20 includes an upper sub 21 having an internally threaded box 22 with which the jar 20 may be united with the pin 23 provided at the lower end of a drill string 24. At its lower end, the jar 20 is provided with a lower sub 25 which is provided with a threaded pin 26 from which other tool elements 27 may be suspended from jar 20. Formed integrally with the lower sub 25 and extending upwardly therefrom is a heavy external sleeve 28 having a smooth bore 29 which is internally threaded at its upper end by heavy tapered threads 30.

Formed integrally with upper sub 21 is a heavy tubular inner mandrel 35 which has approximately a uniform wall thickness throughout its length and extends downwardly through the jar 20 so that the lower externally threaded end portion 36 of said mandrel is disposed at all times within the bore 29 of the lower sub 25.

In the manufacture of the upper sub 21 and mandrel 35 as a single part in the jar 20, the mandrel has a relatively heavy wall thickness which is uniform from the upper sub 21 to the lower threaded end portion 36, with the following exceptions: In the preferred embodiment of the jar 20 illustrated in the drawings this wall thickness is 1% inches and this continues unaltered l5/2 inches downardly from the shoulder 37 of the upper sub 21 formed at the juncture of said hub with said mandrel. For the next 8 inches of the mandrel 35 this is upset to provide, in the following order, an external annular stop 39, a hex section 40 having six flat faces 41 and six arcuate faces 42; a cylindrical section 43 and an externally threaded section 44. For its next 13 /2 inches, the mandrel 35 is uniformly cylindrical with a wall thickness of 1% inches, this portion being designated section 45. The remaining l8 inches between section 45 and the lower threaded end section 36 of mandrel 35 comprises spline section 50 of said mandrel. This section has a uniform wall thickness of 1 /8 inches in which a series of parallel spline grooves 51 are milled.

The short cylindrical section 43 of mandrel 35 has a wall thickness of l 3/16 inches which is the same wall thickness as section 40 has in the areas of the arcuate faces 42. In the radial plane in which sections 40 and 43 meet, an annular series of circumferentially spaced lugs 52 are formed in the material of the mandrel section 40 so as to extend radially above the outer cylindrical surface of section 43 a distance of 0.0075 inches. This produces a maximum wall thickness in section 40 at the points of lugs 52 of 1.195 inches. The outside diameter of the mandrel 35 where the wall thickness of this is IVs equals 4 /2 inches.

Slideably received by the mandrel 35 onto the hexagonal section 40 thereof is a sleeve valve 53 which is preferably formed from a Beryllium-Copper alloy, this valve having an internal diameter allowing it to just clear lugs 52. The valve 53 is about 3 3/16 inches long and has a ground radial face 54 formed on its lower end and an annular series of radial notches 55 formed in its upper end. The sleeve valve 53 is about /2 inches shorter than the axial distance between stop 39 and lugs 52. Also slideably received on the mandrel 35 in assembling the jar 20 is an orificing ring 56 which fits the cylindrical section 43 of said mandrel with a clearance of from 0.001 0.003 inches, the space between said ring and section 40 of the mandrel constituting a dashpot metering orifice 57 for the jar 20. A series of holes 58 formed radially in the lower end portion of ring 56 provide an escape passage for operating oil flowing downwardly through the aforesaid metering orifice 57. The upper surface 59 of orificing ring 56 is ground to make a close sealing fit with the ground face 54 provided on the lower end of sleeve valve 53, the purpose of which will be made clear in the description of the operation.

The lugs 52 extend radially outwardly beyond the cylindrical surface of mandrel section 43 a distance just sufficient to overlie orificing ring 56 and confine it to its position co-extensive with section 43 when the sleeve valve 53 drifts upwardly from the ring 56 as shown in FIGS. 6 and 7.

A retainer nut 60 is next slideably placed over the lower end of the mandrel 35 and screwed onto the threads provided by the externally threaded section 44 of the mandrel to retain orificing ring 56 and sleeve valve 53 in their assembled relations with the mandrel 35.

As shown in FIGS. 1 and 5, the lower threaded end portion 36 of mandrel 35 extends downwardly at all times into the heavy external sleeve 28 which is formed integrally with the lower sub 25. Screwed upwardly onto the lower end of mandrel 35 is a hammer nut 61 which is retained in place by a snap ring 65. The nut 61 makes a close sliding fit with the smooth bore 29 of sleeve 28 and has provided on its upper end a hardened annular hammer face 66.

Slideably applicable upwardly over the mandrel 35 prior to the application of hammer nut 60 to said mandrel is a light-weight dashpot housing sleeve 67 and a spline sub 68 which are connected by threads 69, said sub having external threads at its lower end which screw into the heavy tapered threads 30 provided in the upper end of lower sub 25. The spline sub 68 has a close sliding fit with the spline section 50 of mandrel 35 and has splines 70 extending radially inwardly from the bore of said spline sub which slideably fit into the spline grooves 51 of the mandrel spline section 50.

Provided on the lower end of spline sub 68 is a hardened annular anvil face 71. Also slideably received on the mandrel 35 during the assembly of the jar is a metal floating packing ring 72 having internal and external O-rings 73 and 74 and making a close sliding fit with the cylindrical outer surface of mandrel section 43 and with the internal bore 75 of dashpot housing sleeve 67. Screwed into suitable tapped holes provided in the latter sleeve are plugs 80 for use in filling an annular operating oil chamber 81 enclosed between mandrel 35 and sleeve 67 and located above floating packing ring 72. The external cylindrical surface 82 of the sleeve valve 53 makes a close sealing fit with the bore 75 of sleeve 67 when the jar 20 is collapsed as shown in FIGS. 6-9 for purposes which will be made clear in the description of the operation.

An upper portion of the bore 75 has a counter bore 83 which is fairly shallow but affords ample clearance between said counter bore and the outer surface 82 of valve 53 for free vertical movement of said valve in said counter bore at a time and for a purpose which will also be made clear in the description of the operation.

The upper end of counter bore 83 terminates in another counter bore 84 for receiving a packing 85 for sealing off the upper end of oil chamber 81. This packing includes a two piece junk ring 86 which fits in uper counter bore 84 against a shoulder 87 formed at the lower end thereof; packing material 88 resting on ring 86 and a two piece wear sleeve 89 which fits in the upper end of upper counterbore 84 and makes a close sliding fit both inwardly with the mandrel 35 and outwardly with the upper counter bore 84 of sleeve 67. An upper end portion of wear sleeve 89 is turned down from the outside to provide a shoulder 90 and to receive a collar 95 shaped to fit inwardly over shoulder 90 and be screwed downwardly onto threads 96 which are recessed in the upper outer end portion of sleeve 67 so that collar 95 is flush with the outer surface of sleeve Operation After the jar 20 has been fully assembled as above described, the filling plugs 80, a pair of which are provided in the sleeve 67 at diametrically opposite points therein are removed and the chamber 81 filled with a suitable operating oil after which these plugs are replaced as shown.

As previously pointed out, the jar 20 is designed primarily for use in connection with the drilling of deep wells and to replace those jars previously used in this service which have tended to develop weaknesses resulting from the abuse unavoidable in the drilling of deep wells where the lower portion of the drill string has to bend as the bore hole inclines in one direction or another from vertical. The capacity of the jar 20 to stand up under such abuse is derived from the beefed up mandrel 35 employed therein which is formed integrally with the upper sub 21 and extends without substantial diminution of wall thickness through practically the entire length of the jar so as to terminate within and in close sliding relation with the bore of the heavy external sleeve 28 which is an integral part of the lower sub 25 of the jar. Besides this unification of the structure embodied in the lower portion of the jar while the drilling is going on, this structure is further unitized by the close sliding fit of the mandrel 35 with the spline sub 68 which screws directly downwardly into the lower sub 25.

While the mandrel 35 extends practically entirely downwardly through the other elements embodied in the jar 20, the strength of the upper portion of the mandrel 35 is supplemented very substantially by the stabilizing effect which the floating packing ring 72 has by making a close sliding fit with both the mandrel 35 and the dashpot housing sleeve 67. This is enhanced further by the close sliding fit made by the upper end of dashpot housing sleeve 67 with the mandrel 35 through the upper packing of the jar.

A still further stabilizing action is present in the jar 20, when the jar has collapsed as during a drilling operating, by the sleeve valve 53 making a snug sliding fit externally with the bore 75 of sleeve 67 and having only a few thousandths clearance between the inner surface of the sleeve valve 53 and the six arcuate faces 42 of the hexagonal section 40 of the mandrel 35.

These features indicate how strength and ruggedness have been emphasized in the design of jar 20 while still providing said jar with a highly efficient tensioning dashpot section 97 which is confined to the upper half of the jar whereas the lower half of the jar provides a torque hammer-anvil and jar impact section 98 which is extremely rugged in construction.

The operation of the jar 20 in an emergency requiring the jarring loose of a tool such as a drill bit suspended therefrom will now be described. When this occurs the low 24 to lower the shoulder 37 of the upper sub 21 onto the collar at the upper end of housing sleeve 67, as shown in FIG. 6. When, during the lowering of the mandrel 35 in this manner, the sleeve valve 53 comes to the lower end of the counter bore 83, the friction produced by pressing sleeve valve 53 downwardly into bore 75 of sleeve 67 delays the further downward movement of sleeve valve 53 until stop 39 comes into engagement with the upper end of sleeve valve. This produces a spacing between the ground face 54 in the lower end of sleeve valve 53 and the ground face 59 on the upper endof orifice ring 56. The lugs 52 on the mandrel 35 engage the upper ground face 59 of lower orifice ring 56 so as to cause this to remain in its normal position opposite the cylindrical section 43 of the mandrel 35 and thus continue its downward travel with mandrel 35. When the stop 39 in its downward movement comes into contact with the sleeve valve 53 and starts it into the bore 75 of sleeve 67, a space has been produced between the ground meeting faces of the sleeve valve 53 and the orificing ring 56 so as to allow oil to continue to flow upwardly past the sleeve valve 53, this oil now passing inwardly between the orificing ring 56 and sleeve valve 53 and upwardly through the escape passages provided by the six flat faces 41 in hexagonal section 40 of the mandrel and outwardly from the upper end of said passages through the notches 55 formed in the upper end of sleeve valve 53.

With the parts of the jar 20 thus disposed as shown in FIGS. 6, 7, 8 and 9, and with the sleeve valve 53 disposed deep in the bore 75 of the sleeve 67, the drill string 24 is now placed under an upward strain. This tends to withdraw the mandrel 35 upwardly through the tensioning dashpot section 97. The operating oil in the chamber 81 above sleeve valve 53 is placed under an extremely high pressure because it is unable to escape downwardly between the sleeve valve 53 and the bore 75 confining said sleeve valve because of the tight fit therebetween. The only passageway permitting the compressed operating liquid to escape is the metering orifice 57 between the orificing ring 56 and the cylindrical section 43 of the mandrel 35. This orifice is purposely made to provide an escape of compressed liquid at just that rate which will be adequate to retard the upward withdrawal of the mandrel 35 from its downwardmost position shown in FIGS. 6, 7, 8 and 9 so that the drill rig operator will be able to apply exactly the desired tension on the drill string 24 in a minimum of time for the proper operation of the jar 20 at the moment the sleeve valve 53 travels upwardly so as to be entirely within the counter bore 83 of the sleeve 67. When this moment arrives, the mandrel 35 is no longer restrained from responding to the tremendous tension placed upwardly on the drill string 24 and jumps upwardly in response to said tension through the remaining distance necessary to apply the hammer face 66 to the anvil face 71 with a resounding impact.

To reset the jar 20, the rig operator merely needs to lower the drill string 24 again to return the mandrel 35 to its lowermost position in the jar as shown in FIGS. 6, 7, 8 and 9.

It is desired to point out that the orificing ring 56 does not make a close sliding fit with bore 75 of sleeve 67 so that it is not necessary to make orificing ring 56 of bearing material as is the case with the sleeve valve 53. It is thus possible to employ a high carbon steel for the ring 56 and after the grinding operation to provide the ground face 59, the same is hardened preferably to a rockwell hardness of 36-60. Due to the great tensil strength of the material used in making orificing ring 56, there is no tendency of this ring to yield to the very high hydraulic pressure of the operating oil escaping downwardly through the metering orifice 58 during the tensioning of the jar 20 in a jar stroke. While notches 55 formed in the upper end of the sleeve valve 53 are a convenient way of permitting the escape of operating liquid upwardly past sleeve valve 53 during a resetting movement of the jar 20, it is to be understood that any expedient permitting such escape of operating oil upwardly from within the sleeve valve 53 when the upper end of the latter is in contact with the stop 30 may be employed and be the mechanical equivalent of the notches 55.

When the mandrel 35 moves downwardly through the sleeve valve 53 incidental to resetting the jar for another jarring stroke, it is highly desirable that the orificing ring 56 be held in its normal position opposite the mandrel section 43 and the lugs 52 are provided for accomplishing this purpose. This is effected by the inner diameter of the sleeve valve 53 being slightly greater than the inner diameter of the orificing ring 56 so that the sleeve valve 53 clears the lugs 52 when assembling the jar whereas the orificing ring 56 is unable to do this and is halted by said lugs when the resetting downward motion of the mandrel 35 moves the orificing ring 56 downwardly out of contact with the sleeve valve 53, thereby providing for the operating oil (being compressed in the chamber 31 by the downward travel of sleeve valve 53) to flow inwardly between valve 53 and ring 56 and then upwardly between valve 53 and hexagonal mandrel section 40 and out through the notches 55 in the upper end of valve 53.

I claim:

1. A hydraulic drilling jar comprising an upper sub provided with a threaded box for suspending the jar from the lower end of a drill string;

a lower sub provided with a threaded pin for suspending a tool assembly from said jar, said lower sub terminating integrally upwardly in a heavy external sleeve;

a spline sub, interconnected at its lower end with said lower sub to bare an annular anvil face on the lower end of said spline sub, the bore of said spline sub having splines extending radially inwardly from said bore;

a heavy tubular jar mandrel formed integrally with said upper sub and being integral, with an approximately uniform wall thickness, throughout its length, said mandrel slideably fitting within said spline sub bore and extending down through the spline sub, grooves being provided externally lengthwise where necessary in said mandrel to slideably receive said splines;

hammer means on the lower extending end portion of said mandrel, said means having an annular hardened hammer face exposed upwardly in opposition to said anvil face;

relatively light sleeve means provided on the upper end of said spline sub and extending upwardly in sheathing spaced relation with said mandrel; and

dashpot hydraulic jar tensioning and tripping means mounted in the annular space between said light sleeve means and said mandrel.

2. A jar as recited in claim 1 wherein said lower sub sleeve is internally threaded at its upper end,

said spline sub is externally threaded at its lower end,

said spline sub screws downwardly into said lower sub sleeve, and wherein the bore of said lower sub sleeve exceeds that of said spline sub to provide an annular space between the wall of said lower sub sleeve and said mandrel to accommodate aid hammer means in vertical opposition with said annular anvil face on the lower end of said spline sub.

3. A jar as recited in claim 1 wherein said hammer means comprises an annulus fitting externally on the lower extending end portion of said mandrel; and

means for removably securing said annulus on said mandrel.

4. A jar as recited in claim 2 wherein the lower end portion of said mandrel is externally threaded, and wherein said hammer means comprises an internally threaded nut which screws onto the lower end portion of said mandrel.

5. A jar as recited in claim 1 wherein the jar mandrel is reinforced at spaced points against bending strains imposed during drilling operations by (A) a close co-axial sliding relation between said hammer means and the bore of said lower sub sleeve, (B) by a close co-axial sliding relation between said mandrel and the bore of said spline sub, (C) by a close co-axial sliding relation between a lower sliding seal ring of said dashpot mechanism, said mandrel and said dashpot enclosing sleeve, (D) by a close co-axial sliding relation between a dashpot sleeve valve, said mandrel and said dashpot enclosing sleeve, and (E) by a close co-axial sliding relation between said mandrel, on the one hand, and an upper annular seal of said dashpot mechanism and said dashpot enclosing sleeve, on

the other hand.

6. A jar as recited in claim 1 wherein said dashpot hydraulic jar tensioning and tripping means comprises:

vertically spaced upper and lower seals confining a body of operating oil in an annular chamber disposed between an upper portion of said mandrel and said light weight sleeve;

a sleeve valve;

a sleeve valve stop formed radially from said mandrel and located just below said upper seal, when said jar is in extended position;

said light weight sleeve bore having a counter bore located just below said upper seal;

an orifice ring disposed below and supporting said sleeve valve;

a retainer nut screwed onto threads provided on said mandrel, said nut supporting said ring;

lip means formed on said mandrel and cooperating with said retainer nut to limit the freedom of said ring for vertical movement relative to said mandrel;

said mandrel having lengthwise passages formed externally therein between said stop and said lip means, said mandrel presenting a smooth cylindrical surface under said orifice ring with which surface the bore of said orifice ring makes a slightly loose fit to provide a metered escape orifice during tensioning of said jar,

the abutting faces of said orifice ring and said sleeve valve being ground-to prevent liquid escaping radially therebetween during said jar tensioning;

there being a free radial passage means connecting said escape orifice with the low pressure oil chamber area below said sleeve valve;

said sleeve valve having free passage means at its upper end to allow free passage of oil upwardly from within said valve during retraction of said jar to reset the same for a jarring operation;

said sleeve valve making a loose fit with said counter bore of said light sleeve but a liquid tight fit with the sleeve bore below said counter bore in which said valve functions as a dashpot during the tensioning of the jar.

7. In a hydraulic deep well tool the combination of:

telescopically related internal and external mandrels,

one mandrel having means at its outer end to connect said tool to a drill string, the other mandrel having means at its outer end for suspending other tool elements from said tool;

spline means transmitting torque from one of said mandrels to the other mandrel;

stop means limiting telescopic movement between said mandrels;

vertically spaced .primary and secondary annular seals for confining a body of operating oil in an annular chamber formed between said mandrels and said seals;

a sleeve valve occupying a position in said chamber close to said primary seal when said mandrels are in an extended relation;

a sleeve valve stop means formed radially outwardly from said internal mandrel between said primary seal and one end of said sleeve valve and spaced a short distance from the latter;

said external mandrel having a bore with which said sleeve valve makes a close sliding fit;

an orifice ring abutting the other end of said sleeve valve;

a retainer nut screwed onto threads provided on said internal mandrel-and backing up said orifice ring;

radial lip means formed on said internal mandrel and cooperatingwith said nut to limit vertical movement of said orifice ring relative to said internal mandrel;

said internal mandrel having lengthwise passages formed externally therein between said stop and said lip means;

said internal mandrel presenting a smooth cylindrical surfance between said lip means and said nut, with which surface the bore of said orifice ring makes a slightly loose fit to provide a metered escape orifice during a tensioning telescopic movement in a given direction between said mandrels;

the abutting radial end faces of said orifice ring and said sleeve valve being ground to prevent liquid escaping radially therebetween during said tensioning movement;

a free radial passage being provided connecting said escape orifice with the low pressure area of said oil chamber;

passage means being provided for the escape upwardly of oil trapped between said mandrel, said stop and said sleeve valve when said stop is engaged by said valve during a relaxing telescopic movement in an opposite direction between said mandrels.

8. In a telescopic oil well tool, the functioning of which depends upon hydraulic damping of relative axial movement between the telescopic parts thereof in a given direction, the combination of:

an internal mandrel;

an external mandrel telescopically receiving said internal mandrel and spaced therefrom to provide an annular operating oil chamber therebetween;

axially spaced annular seal means sealing off upper and lower ends of said chamber;

axially spaced upper and lower valve stops extending radially externally from said inner mandrel;

an orifice ring closely spaced from said internal mandrel and resting on said lower stop, there being a cylindrical external face on said internal mandrel co-extensive axially with said ring to form a dashpot orifice between said face and the bore of said ring;

means cooperating with said lower stop to confine said ring in axially juxtaposed relation with said face;

a sleeve valve surrounding said internal mandrel between said ring and said upper stop and having free play to shift vertically therebetween, said valve having a liquid tight sliding fit with the bore of said external mandrel, the abutting ends of said ring and valve having true radial ground faces preventing escape of oil radially between said valve and ring when said ring is lifted against said valve by pulling upwardly on said internal mandrel, there being oil escape passages formed lengthwise externally in said internal mandrel between said upper stop and said orifice ring, there also being passage means allowing oil to escape upwardly from said oil escape passages when said valve is caused to engage said upper stop when said internal mandrel is telescopically lowered in said external mandrel. 

1. A hydraulic drilling jar comprising an upper sub provided with a threaded box for suspending the jar from the lower end of a drill string; a lower sub provided with a threaded pin for suspending a tool assembly from said jar, said lower sub terminating integrally upwardly in a heavy external sleeve; a spline sub, interconnected at its lower end with said lower sub to bare an annular anvil face on the lower end of said spline sub, the bore of said spline sub having splines extending radially inwardly from said bore; a heavy tubular jar mandrel formed integrally with said upper sub and being integral, with an approximately uniform wall thickness, throughout its length, said mandrel slideably fitting within said spline sub bore and extending down through the spline sub, grooves being provided externally lengthwise where necessary in said mandrel to slideably receive said splines; hammer means on the lower extending end portion of said mandrel, said means having an annular hardened hammer face exposed upwardly in opposition to said anvil face; relatively light sleeve means provided on the upper end of said spline sub and extending upwardly in sheathing spaced relation with said mandrel; and dashpot hydraulic jar tensioning and tripping means mounted in the annular space between said light sleeve means and said mandrel.
 2. A jar as recited in claim 1 wherein said lower sub sleeve is internally threaded at its upper end, said spline sub is externally threaded at its lower end, said spline sub screws downwardly into said lower sub sleeve, and wherein the bore of said lower sub sleeve exceeds that of said spline sub to provide an annular space between the wall of said lower sub sleeve and said mandrel to accommodate aid hammer means in vertical opposition with said annular anvil face on the lower end of said spline sub.
 3. A jar as recited in claim 1 wherein said hammer means comprises an annulus fitting externally on the lower extending end portion of said mandrel; and means for removably securing said annulus on said mandrel.
 4. A jar as recited in claim 2 wherein the lower end portion of said mandrel is externally threaded, and wherein said hammer means comprises an internally threaded nut which screws onto the lower end portion of said mandrel.
 5. A jar as recited in claim 1 wherein the jar mandrel is reinforced at spaced points against bending strains imposed during drilling operations by (A) a close co-axial sliding relation between said hammer means and the bore of said lower sub sleeve, (B) by a close co-axial sliding relation between said mandrel and the bore of said spline sub, (C) by a close co-axial sliding relation between a lower sliding seal ring of said dashpot mechanism, said mandrel and said dashpot enclosing sleeve, (D) by a close co-axial sliding relation between a dashpot sleeve valve, said mandrel and said dashpot enclosing sleeve, and (E) by a close co-axial sliding relation between said mandrel, on the one hand, and an upper annular seal of said dashpot mechanism and said dashpot enclosing sleeve, on the other hand.
 6. A jar as recited in claim 1 wherein said dashpot hydraulic jar tensioning and tripping means comprises: vertically spaced upper and lower seals confining a body of operating oil in an annular chamber disposed between an upper portion of said mandrel and said light weight sleeve; a sleeve valve; a sleeve valve stop formed radially from said mandrel and located just below said upper seal, when said jar is in extended position; said light weight sleeve bore having a counter bore located just below said upper seal; an orifice ring disposed below and supporting said sleeve valve; a retainer nut screwed onto threads provided on said mandrel, said nut supporting said ring; lip means formed on said mandrel and cooperating with said retainer nut to limit the freedom of said ring for vertical movement relative to said mandrel; said mandrel having lengthwise passages formed externally therein between said stop and said lip means, said mandrel presenting a smooth cylindrical surface under said orifice ring with which surface the bore of said orifice ring makes a slightly loose fit to provide a metered escape orifice during tensioning of said jar, the abutting faces of said orifice ring and said sleeve valve being ground to prevent liquid escaping radially therebetween during said jar tensioning; there being a free radial passage means connecting said escape orifice with the low pressure oil chamber area below said sleeve valve; said sleeve valve having free passage means at its upper end to allow free passage of oil upwardly from within said valve during retraction of said jar to reset the same for a jarring operation; said sleeve valve making a loose fit with said counter bore of said light sleeve but a liquid tight fit with the sleeve bore below said counter bore in which said valve functions as a dashpot during the tensioning of the jar.
 7. In a hydraulic deep well tool the combination of: telescopically related internal and external mandrels, one mandrel having means at its outer end to connect said tool to a drill string, the other mandrel having means at its outer end for suspending other tool elements from said tool; spline means transmitting torque from one of said mandrels to the other mandrel; stop means limiting telescopic movement between said mandrels; vertically spaced primary and secondary annular seals for confining a body of operating oil in an annular chamber formed between said mandrels and said seals; a sleeve valve occupying a position in said chamber close to said primary seal when said mandrels are in an extended relation; a sleeve valve stop means formed radially outwardly from said internal mandrel between said primary seal and one end of said sleeve valve and spaced a short distance from the latter; said external mandrel having a bore with which said sleeve valve makes a close sliding fit; an orifice ring abutting the other end of said sleeve valve; a retainer nut screwed onto threads provided on said internal mandrel and backing up said orifice ring; radial lip means formed on said internal mandrel and cooperating with said nut to limit vertical movement of said orifice ring relative to said internal mandrel; said internal mandrel having lengthwise passages formed externally therein between said stop and said lip means; said internal mandrel presenting a smooth cylindrical surfance between said lip means and said nut, with which surface the bore of said orifice ring makes a slightly loose fit to provide a metered escape orifice during a tensioning telescopic movement in a given direction between said mandrels; the abutting radial end faces of said orifice ring and said sleeve valve being ground to prevent liquid escaping radially therebetween during said tensioning movement; a free radial passage being provided connecting said escape orifice with the low pressure area of said oil chamber; passage means being provided for the escape upwardly of oil trapped between said mandrel, said stop and said sleeve valve when said stop is engaged by said valve during a relaxing telescopic movement in an opposite direction between said mandrels.
 8. In a telescopic oil well tool, the functioning of which depends upon hydraulic damping of relative axial movement between the telescopic parts thereof in a given direction, the combination of: an internal mandrel; an external mandrel telescopically receiving said internal mandrel and spaced therefrom to provide an annular operating oil chamber therebetween; axially spaced annular seal means sealing off upper and lower ends of said chamber; axially spaced upper and lower valve stops extending radially externally from said inner mandrel; an orifice ring closely spaced from said internal mandrel and resting on said lower stop, there being a cylindrical external face on said internal mandrel co-extensive axially with said ring to form a dashpot orifice between said face and the bore of said ring; means cooperating with said lower stop to confine said ring in axially juxtaposed relation with said face; a sleeve valve surrounding said internal mandrel between said ring and saId upper stop and having free play to shift vertically therebetween, said valve having a liquid tight sliding fit with the bore of said external mandrel, the abutting ends of said ring and valve having true radial ground faces preventing escape of oil radially between said valve and ring when said ring is lifted against said valve by pulling upwardly on said internal mandrel, there being oil escape passages formed lengthwise externally in said internal mandrel between said upper stop and said orifice ring, there also being passage means allowing oil to escape upwardly from said oil escape passages when said valve is caused to engage said upper stop when said internal mandrel is telescopically lowered in said external mandrel. 